Ultra sensitive torque motors



Oct. 11, 1966 A. J. HILGERT 3,278,873

ULTRA SENSITIVE TORQUE MOTORS Filed Aug. 13, 1964 2 Sheets-Sheet 1 I INVENTOR ADOLPH J. HILGERT ATTORNEYS 1966 A. J. HILGERT 3,278,873

ULTRA SENSITIVE TORQUE MOTORS Filed Aug. 13, 1964 2 Sheets-Sheet 2 4vD 47 k 5/ SUPPLY 58 52 4 #3 i?,,,lT

VOTLT E OUTPUT BY 5 7 53 W AT TORNEYS INVENTOR 55 ADOLPH J. HILGERT United States Patent 3,278,873 ULTRA SENSITIVE TORQUE MOTORS Adolph J. Hilgert, Milwaukee, Wis., assignor to Johnson Service Company, Milwaukee, Wis., a corporation of Wisconsin Filed Aug. 13, 1964, Ser. No. 389,435 7 Claims. (Cl. 335230) This invention relates tive torque motors, motor which is well relay actuator.

Heretofore some power units have comprised a conventional, permanent magnet with a coil mounted to move in the magnetic field. This prior design has a high degree of linearity but has little efliciency in converting electric energy into force. As a result, it must be made relatively large to accomplish any work, or some intermediate stage of amplification between the signal and motor must be used. In these conventional designs longer coils, or a stronger permanent magnetic field from a larger permanent magnet could produce a stronger force from a given input signal. Within reasonable size limitations this prior type of power unit does not have the required sensitivity to operate directly from a weak signal.

A more eflicient type of device which is known as a torque motor has greater sensitivity and is able to operate from a much weaker signal. The ultimate force output of torque motors is limited only by the saturation of the magnetic circuit or parts thereof.

A general object of the present invention is to keep the physical dimensions of a torque motor small while maintaining a high ratio of force output to electrical input.

A further object of the present invention is to provide a torque motor wherein there is a minimum length of air gap between armature and pole faces; a maximum number of turns for the allowable coil resistances.

A further object of the present invention is to keep the length of the magnetic circuit as short as possible to minimize hysteresis and still maintain a high ratio of number of turns to coil resistance.

A further object of the present invention is to provide a device which may, if desired, be responsive to a multiplicity of input signals to integrate said signals in various manners.

A further object of the invention is to provide an improved torque motor of relatively simple design which is, nevertheless, highly sensitive and eflicient, and capable of allowing wide impedance variations, the unit being of such construction that it is easy to produce, and the design of which makes it easy to maintain a small air gap between the armature and the pole faces.

A further object of the invention is to provide an improved torque motor having a unique means of polarization to introduce an initial flux and force into the working air gap, by which the force output is linearly proportional to the ampere turns, the design being one in which the pole faces may be accurately located in a single plane so that the working air gap may be readily set to a small value, resulting in the maximum obtainable sensitivity, and the design further being such as to maintain the mean flux path through the air gap parallel to the axis of rotation for the armature-carrying lever, the magnetic pull acting through an effective torque lever of constant length on each side of the pivot.

While the torque motor of my co-pending application, Serial No. 228,997, filed October 8, 1962, now abandoned, has all of the above advantages, the present invention is an improvement upon the design of the torque moto improvements in ultra sensiand more particularly to a torque adapted for use as an ultra sensitive is better suited for certain types of uses.

A specific object of the torque motor of this present! invention is to provide a novel design for a four-core motor, which design permits the eflicient use of a single permanent magnet for both pairs of cores thereby simplifying the design and lowering the cost of production.

A further more specific object of the invention is to provide a novel design for a torque motor embodying two pairs of cores, wherein one core of one pair is joined to the opposite core of the other pair by a separate base member on each side to provide common flux paths. This is to be distinguished from constructions where each base member joins the cores of a pair.

With the above and other objects in view, the invention consists of the improved ultra sensitive torque motor, and all of its parts and combinations, as set forth in the claims, and all equivalents thereof.

In the accompanying drawings illustrating one complete embodiment of a preferred form of the invention, including one use thereof, in which the same reference numerals designate the same parts in all of the views:

FIG. 1 is a top plan view of the improved torque motor showing how it may be used in a pressure-electric transducer;

FIG. 2 is a sectional the line 22 of FIG. 1;

FIG. 3 is a sectional view taken approximately on the line 3-3 of FIG. 2;

FIG. 4 is a diagrammatic view showing the wiring for the different sets of coils; and

FIG. 5 is a wiring diagram for the entire circuit.

Referring now to FIG. 1, there are spaced parallel elongated base members 11 and 12 formed of suitable metal. One pair of cores comprises the cores 13 and 14, and the core 13 has its lower end swaged into the base 11, and the core 14 its lower end swaged into the other base 12. Similarly, another pair of core members comprises the cores 15 and 16, the core 15 being swaged into the base member 11 and the core 16 into the base member 12. Thus, each base member connects opposite cores of the pairs, and it is to be noted that there is no non-magnetic gap between the lower ends of the cores and the base members as is present in the design of my co-pending application, Serial No. 228,997.

The cores are each wound with coils as indicated at 17, 18, 19 and 20 in FIG. 4. The design makes it practical to have relatively small cores so that a maximum number of turns for the allowable coil resistances is possible.

The pair of cores 1314 is adapted to coact with an armature 21, and the pair of cores 15-16 with an armature 22. The hysteresis is kept to a minimum by the use of low hysteresis core material and base material, preferably an nickel alloy, such as Carpenter HYMU 80 or Allegheny Mumetal. The design is such that it is a relatively simple matter to keep all of the upper pole faces flat and in a single plane and, inasmuch as these faces are all in a single plane, the structure is relatively simple to produce by means of a common grinding operation. The accurate location of the pole faces in a single plane allows the working air gaps 23 for one pair and 24 for the other pair to be set at small values. This results in the maximum obtainable sensitivity from this factor. The shorter the gaps 23-24 the better, but fo practical purposes, it is diflicult to have a working gap of less than .002 inch. If the working gap exceeds .010 inch, the main advantages of the present invention are dissipated. For practical purposes the air gaps are maintained between .004.008 inch. Pole face enlargements may readily be attached to the upper ends of the cores view taken approximately on as desired without requiring any significant change in the magnetic structure.

As a feature of the present invention a polarizing or biasing permanent magnet 26 connects the base 11 with the base 12 and is located between the pairs of cores and ,parallel to the armatures 21 and 22. The present design I-makes it practical to utilize a single polarizing magnet to lserve both pairs of cores, whereas with the construction of my co-pending application, Serial No. 228,997, where two pairs of cores are used on opposite sides of a pivot, each pair of cores must have its own polarizing magnet.

The armatures may be movably supported in any suitable way. One such way is illustrated in FIGS. 1 and 2, wherein there is a lever 27, preferably of aluminum and preferably U-shaped in cross-section, which is supported to pivot on an axis which extends transversely of the base members 11 and 12 and which is located between the pairs of cores 13-14 and 1516. Whenever linearity between the input and output of the device is required, the location of the pivot is mid-way between the pairs of cores as illustrated. With this arrangement the armatures 21 and 22 are suitably connected to the lower faces of the lever 27 as illustrated. In this design it is to be noted that the cores and, therefore, the length and diameter of the coils 17, 18, 19 and 20 are independent of armature dimensions.

In FIGS. 1, 2 and 3 the torque motor is shown as a part of a pressure-electric transducer. This, however, is only one possible use for the improved torque motor. This transducer includes a suitable supporting base 29 on which the magnet bases 11 and 12 are supported. In addition, the base supports spaced posts 30. To the upper ends of the posts is a flexure hinge 31 which is L-shaped in cross-section and which has a vertical flange secured to the posts and a horizontal flange secured to the under side of the lever 27. This provides the hinge for mounting the lever to pivot on the axis 28.

The base also supports a pressure actuator 32 having an internal pressure chamber 33 for receiving a pressure fluid from an inlet conduit 34. Variations in pressure, constituting the signal from an external source such as a pneumatic thermostat, is admitted to the chamber 33 through the inlet 34 to act on a diaphragm 35. The latter in turn acts on the lower end of a spring 36, and the upper end of the spring is seated against the head of an adjustment screw 37 which is threadedly supported in the transfer lever 27. Another adjustment screw 38 at the end of the transfer lever coacts with the end of a screw 39 to form an adjustable stop.

At the opposite end of the transfer lever an upper contact member 40 is adjustably carried. Bonded to the lower end of the contact member is a carbon disc 41. Suitably supported in and projecting upwardly from the base 29 is a lower contact member 42 having a carbon disc 43 bonded to its upper end. A flexible damping sleeve 44 surrounds the meeting ends of the upper and lower contacts and the carbon discs. With this arrangement, when no pressure is being applied to the contacts the carbon discs 41 and 43 are barely in contact, or very slightly separated, so that there is a high resistance to the flow of electricity. When pressure is applied, however, to the carbon discs, the resistance to the flow of current decreases proportionately to the amount of pressure. Flow of current from the source through the coils 17, 18, 19 and 20 is under the control of these contacts, as will be hereinafter explained more fully.

By referring to FIG. 4 it is to be noted that there is a split flux from the permanent magnet 26, with one flux path passing from the North pole of the permanent magnet, through a portion of the base member 11, through the core 13, through the armature by way of the air gaps, down through the core 14, through a portion of the base 12, and back to the South pole of the permanent magnet 26, as is illustrated in the lower portion of FIG. 4. Another flux path travels similarly from the permanent magnet through the other pair of cores 1516 and the armature 22, as is illustrated in the upper portion of FIG. 4. It is to be noted that the mean flux path through the air gaps 23 and 24 is parallel to the pivot axis 28 of the flexure hinge 31 for the armature lever 27. In conventional designs this path is usually across such an axis. It is to be noted also that the magnetic pull acts through an effective torque lever of constant length on each side of the pivot 31.

FIG. 4 shows that the coils 17, 18, 19 and 20 are so connected in the electric circuit and to each other as to cause the flux on one side of the pivot 31 to so coact with the flux on the other side of the pivot as to produce a torque on the lever 27. Specifically, referring to FIG. 4, the coils 17 and 18, which are below the armature 21, are wired in a reverse direction with respect to the positive and negative sides of the supply current than the coils 19 and 20.

Operation In operation the supply voltage from the wires 45 and 46 (FIG. 5) is through the carbon contacts 41 and 43, with the coils 17, 18, 19 and 20 being generally, but not necessarily, in parallel with one another (as is generally illustrated in FIG. 4). The detailed interconnections of the coils in the circuit and with one another are difficult to show in a diagram such as FIG. 5, so FIG. 4 has been employed to illustrate the specific wiring of the coils with one another and with reference to the positive and negative sides of the current supply. The circuit also includes a potentiometer 47 for calibrating purposes and a current limiting resistor 58. Since the current through coils 17, 18, 19 and 20 is exactly proportional to the input pressure and since the total current through these coils flows through precision resistor 48, the voltage developed across this resistor is exactly proportional to the input pressure. Resistor 51 and condenser 52 correct for a lagging current in coils 17, 18, 19 and 20 so that the input force and magnetic feedback force are essentially in phase thereby preventing any induced electro-mechanical oscillation of the system.

When air or other fluid is applied under pressure through the fitting 34 into the chamber 33, a force is exerted upwardly on the right-hand side of the lever '27. This causes the opposite end of the lever to move downwardly, which tends to compress the carbon discs 4143 to a greater or lesser degree, depending upon the pneumatic force exerted, and causes current to flow through the windings 17, 18, 19 and 20 of the torque motor. However, as soon as current flows through the torque motor there is an action in the nature of a negative feedback torque from the magnetic flux, and there is ultimately a force balance established between the action of the pneumatic force and the action of the torque motor. The higher the input force of the compressed air into the chamber 33, the greater the amount of current which fiows through the coils and, therefore, the higher the output voltage from the conductors 4653. On a decrease in pressure in the chamber 33 a reverse action takes place.

The pair of coils 17-18 on one side of the hinge 31 has the current flowing in such a direction as to oppose the flux of the permanent magnet to decrease the total flux through the cores 13-14 as the pressure in the chamber 33 increases. Simultaneously the coils 19 and 20 have current flowing in such a direction as to add to the flux of the permanent magnet so that the total flux increases through the cores 15-16.

Thus when the torque motor is used in conjunction with a pressure-electric transducer, as shown in the illustrated exemplification, there is an output through the wires 46-53 which is substantially independent of supply voltage and load variations. Since little motion takes place, the initial sensitivity is extremely high, so that enough feedback can be employed to produce stable operation.

While the improved torque motor has been shown for purposes of illustration as employed in a pressure-electric transducer, it is obvious that the torque motor proper can be used in various combinations where it is desirable to keep the physical dimensions of a torque motor small while maintaining a high ratio of force output to electrical input. When operating as a torque motor alone, without any pneumatic influence from a pneumatic device such as the actuator 32, the Wiring arrangement shown in FIG. 4 causes the flux on one side of the pivot to coact with the flux on the other side of the pivot to produce a torque on the lever 27, and said arrangement may be employed in various types of devices. When the device is used in a pressure-electric transducer, however, a force balance is ultimately established between the pneumatic force and the torque action of the motor.

Various changes, modifications, and other adaptations may be made without departing from the spirit of the invention, and all of such changes are contemplated as may come within the scope of the claims.

What I claim is:

1. A torque motor comprising spaced pairs of electromagnets, each pair including spaced cores with pole faces and there being coil means on at least one core, a base member magnetically connecting the core of one pair with the opposite core of the other pair on one side, a second base member magnetically connecting the other core of the one pair with the opposite core of the other pair on the other side, an armature for the cores of each pair of electromagnets, means pivoted between said pairs of electromagnets supporting one armature on one side of the pivot and the other armature on the other side of the pivot with the axis of the pivot extending generally parallel to the armatures, said supporting means being so positioned as to provide air gaps of very short length between the armatures and the adjacent pole faces, a permanent magnet positioned between the pairs of electromagnets and having one end connected to one base member and the other end connected to the other base member, and arranged to produce a split magnetic flux,

one part of which is adapted to pass through the cores of one pair of electromagnets and through the adjacent armature, and the other part of which is adapted to pass an electric circuit, said coil means for the cores being so connected in the circuit as to cause the flux on one side of the pivot for the armature supporting means to coact with the flux on the other side of said pivot to produce a torque in the lever.

2. A torque motor as defined in claim 1 wherein the axis of the pivot for the armature-supporting means is located midway between the armatures.

3. A torque motor as defined in claim 1 wherein the permanent magnet is positioned midway between the pairs of electromagnets.

4. A torque motor as defined in claim 1 wherein the axis of the pivot for the armature-supporting means is located midway between the a-rmatures and wherein the permanent magnet is positioned midway between the pairs of electromagnets.

5. A torque motor as defined in claim 1 in which the permanent magnet is an inverted U in shape.

6. A torque motor as defined in claim 1 in which the base members for the cores extend parallel to one another and at right angles to the armatures.

7. A torque motor as defined in claim 1 in which the permanent magnet extends generally parallel to the armatures.

References Cited by the Examiner UNITED STATES PATENTS 2,526,685 10/1950 Price 3l7-172 3,227,840 1/1966 Reed et al 317l7l X BERNARD A. GILHEANY, Primary Examiner. G. HARRIS, IR., Assistant Examiner. 

1. A TORQUE MOTOR COMPRISING SPACED PAIRS OF ELECTROMAGNETS, EACH PAIR INCLUDING SPACED CORES WITH POLE FACES AND THERE BEING COIL MEANS ON AT LEAST ONE CORE, A BASE MEMBER MAGNETICALLY CONNECTING THE CORE OF ONE PAIR WITH THE OPPOSITE CORE OF THE OTHER PAIR ON ONE SIDE, A SECOND BASE MEMBER MAGNETICALLY CONNECTING THE OTHER CORE OF THE ONE PAIR WITH THE OPPOSITE CORE OF THE OTHER PAIR ON THE OTHER SIDE, AN ARMATURE FOR THE CORES OF EACH PAIR OF ELECTROMAGNETS, MEANS PIVOTED BETWEEN SAID PAIRS OF ELECTROMAGNETS SUPPORTING ONE ARMATURE ON ONE SIDE OF THE PIVOT AND THE OTHER ARMATURE ON THE OTHER SIDE OF THE PIVOT WITH THE AXIS OF THE PIVOT EXTENDING GENERALLY PARALLEL TO THE ARMATURES, SAID SUPPORTING MEANS BEING SO POSITIONED AS TO PROVIDE AIR GAPS OF VERY SHORT LENGTH BETWEEN THE ARMATURES AND THE ADJACENT POLE FACES, A PERMANENT MAGNET POSITIONED BEWTWEEN THE PAIRS OF ELECTROMAGNETS AND HAVING ONE END CONNECTED TO ONE BASE MEMBER AND THE OTHER END CONNECTED TO THE OTHER BASE MEMBER, AND ARRANGED TO PRODUCE A SPLIT MAGNETIC FLUX, ONE PART OF WHICH IS ADAPTED TO PASS THROUGH THE CORES OF ONE PAIR OF ELECTROMAGNETS AND THROUGH THE ADJACENT ARMATURE, AND THE OTHER PART OF WHICH IS ADAPTED TO PASS THROUGH THE CORES OF THE OTHER PAIR OF ELECTROMAGNETS AND THROUGH THE ARMATURE THEREFOR, SAID FLUXES BEING ADAPTED TO COACT WITH THE FLUXES PRODUCED BY THE COIL MEANS, AND AN ELECTRIC CIRCUIT, SAID COIL MEANS FOR THE CORES BEING SO CONNECTED IN THE CIRCUIT AS TO CAUSE THE FLUX ON ONE SIDE OF THE PIVOT FOR THE ARMATURE SUPPORTING MEANS TO COACT WITH THE FLUX ON THE OTHER SIDE OF SAID PIVOT TO PRODUCE A TORQUE IN THE LEVER. 